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I am being challenged by a math problem that I need addressed by someone who is good at math and knows about motor vehicles. Can you help?

So my truck that I use for business purposes has the wrong size tires on it. I am trying to figure out gas mileage; but I can't get an accurate outcome because the tires are wrong size. Speedometer reads faster than what vehicle is really going. The odometer is not accurate as well. The tires I do have are P215/70/R14. The tires that I should have to get accurate reads is P215/75/R14. If you have answer to this; please keep it in basic algebraic terms, or basic mathematics. There has to be an adjustment I can make to odometer reading; without having to go out and buy new tires...spending hundreds of dollars. Can you help?

2 Answers

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  • Anonymous
    2 months ago

    Use the gps on your phone to get a speed reading and correct from there. No, it's not scientific or mathematic but tires don't always live up to their measurements so gps is better from a quick and dirty point of view.

    • ugiidriver
      Lv 7
      2 months agoReport

      Doing the algebra has the advantage of knowing the correction factor for future use,, how far did that set of tires last, how much to adjust the oil change interval, etc.

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  • L.N.
    Lv 7
    2 months ago

    Diameters are 25.85 and 26.70 respectively. 

    26.70/25.85 = about 1.033 so multiply your odometer mileage by 1.033 to correct for tire size before you divide by gallons used.

    On second thought, divide mileage  by 1.033 since your speedo is fast.

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    • ugiidriver
      Lv 7
      2 months agoReport

      The second thought is correct, Since the newer tires have a smaller circumference, you are not going as far as your odometer reads. The odometer reading needs to be reduced.

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